Preparation of amides



Patented May 26, 1953 2,640,077 PREPARATION OF AMIDES Marcus A. Naylor, Jr., Wilmington, Del., assignor to E. 1. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application March 9, 1951, Serial No. 214,840

14 Claims.

This invention relates to the preparation of aliphatic carboxylic acid amides from dialkyl sulfides, ammonium polysulfide and water. This application is a continuation-in-part of my copending application S. N. 185,907 (now abandoned) filed September 20, 1950, in which I have disclosed that the olefin-sulfur oils obtained as by-products in the formation of amides from olefins and aqueous ammonium polysulfide can be recycled with a further quantity of aqueous ammonium polysulfide at 200 to 350 6., whereby an additional quantity of amide is produced. "These olefin-sulfur oils are composed of dialkyl sulfides.

An object of the present invention is to convert dialkyl sulfides to amides.

This object is accomplished by reacting such sulfides with aqueous ammonium polysulfide under the conditions here'inbelow set forth at a temperature between 180 C. and 340 C. In particular embodiments, the present invention comprises heating together a dialkyl sulfide containing from 6 to 13 carbon atoms per molecule with aqueous ammonium polysulfide at a temperature between 240 C. and 340 C.

Instead of introducing ammonium polysulfide as such, it is frequently practical and expedient to introduce a mixture which is produced by adding powdered sulfur to aqueous ammonia.

In apreferred method for practicing the invention the dialkyl disulfide which is employed is the alkene-sulfur oil which is produced as a by-product in the synthesis of amides from alkenes and aqueous ammonium polysulfide. Thus the invention can be practiced by heating a reaction mixture comprising an alkene and aqueous ammonium polysulfide at a temperature within the range of 140 C. to 300 C. whereby an alkanoic acid amide and an alkene-sulfur oil are obtained, separating alkanoic acid amide and alkene-sulfur oil from the resulting mixture, and thereafter heating the said alkene-sulfur oil at a temperature within the range of 180 C. to 340 C. in a reaction mixture comprising aqueous ammonium polysulfide whereby an additional quantity of alkanoic acid amide is obtained, and separating the said alkanoic acid amide from the resulting mixture. The invention also can be practiced by heating any dialkyl sulfide (e. g. a dialkyl monosulfide, dialkyl disulfide, dialkyl trisulfide, etc.) in a reaction mixture comprising aqueous ammonium polysulfide in this manner.

Any alkene may be employed in making the alkene-sulfur oil, but particularly advantageous results are obtained when the alkene is propylene or isobutylene; the amides produced from these specific olefins are propionamide and isobutyramide respectively. Other suitable alkenes include ethylene, n-butenes, pentenes, hexenes, 3,5,5-trimethylhexenes, diisobutylene, dodecenes, octadecenes and the like.

The alkene-sulfur oils may be prepared by employing, instead of ammonia, any primary or secondary amine, but it is usually preferred to employ ammonia. If N-alkyl amides are desired, primary or secondary alkyl amines may be used in place of ammonia in the conversion of the organic sulfides to amides. In recycling an alkeno-sulfur oil with make-up alkene, it is preferred to employ initially at least 1.5 mols of free and combined ammonia per mol of alkene and at least 2 mols of water per mol of alkene. The optimum molar ratio of water: alkene is at least 2 and preferably no greater than 6. The quantity of alkene-sulfur oil to be recycled will of course depend upon the quantity produced as by-produot, and this depends largely upon the reaction temperature as explained hereinafter in greater detail. The total quantity of free and combined'sulfur is preferably from 2 to 6 mols per mol of olefin; the theoretical quantity (2 mols per mol of olefin) may be used, but it is generally better to introduce an excess of sulfur, so as to obtain optimum yields and reaction rates.

Hydrogen sulfide is preferably introduced into the reaction mixture in sufiicient quantity to solubilize the sulfur in the aqueous ammoniacal solution. About 0.13 to 1.0 mol of hydrogen sulfide is preferably employed per mol of free sulfur introduced. This applies both to the process of producing alkene-sulfur oils, and the step of converting them to amides.

Any suitable reaction vessel may be employed in the practice of this invention. A tubular reactor composed of a coil of stainless steel tubing surrounded by a suitable liquid heat transfer medium gives excellent results. When such a reaction vessel is employed the reactants may be fed from individual containers and mixed in the feed lines before entering the reactor. Preferably, however, one of the reactants, e. g. the alkene, is injected separately so as to prevent the reaction from taking place until the preferred reaction conditions are obtained. In a preferred embodiment involving recycling an alkene-sulfur oil, a homogeneous solution is produced by mixing liquid ammonia and hydrogen sulfide with Water, heating the mixture to a temperature above 120, and adding sulfur thereto to produce the desired mol ratio of the necessary ingredients, as set forth above. This mixture can be preheated and injected into the tubular reactor while injecting preheated propylene (or other alkene) by means of a separate pump. The reaction product which emerges irom the tubular reactor is' dischargedninto a gas-liquid separator.

TABLE I Recycling propylene-sulfur oil in synthesis of propz'onamide' from propylene Mol RatiosinFeed Stream Yields 7 7 e I V #lhr. Percent Reaction Tem- Pressure Total Oil in perature, 01' (p s-1i.)- 1 V Thru- Amide, Acid, Liquid 03H CaH H20 NHa S HzS put Percent Percent Product on OaHa on C2110 3, 000 l O. 05 2. 71 1. 45 2. 24 0. 39 21. 4 40 2-4 40-50 3, 000 1 0. 05 2. 64 1. 57 2. 40 0. 50 22.3 57 0. 17 3, 1 0. 2. 79' 1.47 2. 37 0. 47 22.1 71. 0; 0 1-2 3, 000 v 1 0. 04 2. 77 1. 40 2. 30 0. 62 22.1 49 2. 5

The following materials are'found. in'theliquid phase thus produced: propionamide, ammonium. propionate, ammonium polysulfide ammonium hydrosulfide, ammonium hydroxide; water and alkene-sulfur oils. Thegaseous: components. of

thereaction mixture arealkanes (whenpresent as components ofv the alkene' feed), ammonia, hydrogen sulfide, .water, .and a-ismall amount: of the more volatile alkene sulfur oils; The separa' tion of the gaseous andliquidphases can be carriedout at atmospheric pressure. and atateme peratureof about 25? to 100 C'., preferably. about 50 C. Alternatively, the-separation can. be carried outat superatmos'pheric' pressures? andv at temperatures in the rangeiof 'about.l00 C. .to.

200? G. Moreover, if2desired.theipressureunaybev 40 substantially the same asthe. pressure which. is employed in-the reaction vessel. If.:desired;.the liquid'stream from the gas-liqnidlseparator can:- be. run to a stripping column and. amoverhead stream consisting. of water, ammonium. hydroesulfide, alkene-sulfur: oils, and :smallzamountsiof;

all of the steam-volatile:alkeneesulfur: oils have:

been removed from. the propionamicle. The dis.-

tillation residue contains. a mixture: of alkanoicacid amide, somealkanoic acid; and alkene-sulfur. oils: together with a certainamountf o f-sulfur If desired; at this stage additional water can;

be. added, and the distillation can. be: resumedi Finally, a propionamide. cut .issobta-ined :at-a tem; perature of about.110 0., andapressure-of: 20 mm. A small amount of tarryvresiduememains in the distillation vessel.

The invention. is. illustrative further. by means of. the following examples.

Example. 1 .-Propylene-, water. ammonia sule fur and hydrogen sulfiddwere. passedthrough' a tubular reactionyessel. (55 feet-..of5 coiled .tubing, 75

Example 2.The following reaction mixture was passed through a tubular reaction vessel :at. a temperaturebetween 277 and 294 C. under a.

pressure of 3,000 lbs/sq; in.

Feed Pounds/hone Propylene-sulfur oil 6..41 Men. 4.98 Ammonl 2:58 Sulfur..." 4.00 Hydrogen sulfide 2.18

Total feed 20.21

An analysis of the crude reaction productsshowed theformation of 3.63 pounds perhour of propionamide. feed=contained-2.4% by weightof propionamide, the actual production of propionamide resulting from the conversion of oils was 3.47 pounds per hour of 1 amide.

carried-out in a pressure tube lined with stainless-steel. Agitation of the tube was accomplished by placing it in a rocker assembly equipped with band heaters.

A mixture of'59 partsof di-n-propylmonosulfide (0.5'mol), 70.5 parts of sulfur (2.2 mols), 23.8 parts of ammonia (1.4 mols), and 49.5 parts of water (2.75 mols) was introduced into the tubeand the mixture'was agitated-for one hour at250'to 264 C. The tube was cooled to room temperature, and the gaseous products essentially composed-of hydrogen sulfide were bled off. A.

lightbrown liquid product (127 parts.) was. re-

moved'from the pressure tube, and the tube was Washed with Water which was added to the crude liquid product.

The liquid product was extracted withisopentane', and 6.2 parts of an oil was-obtainedupon. evaporation. The aqueous layercontaining 216- parts was distilled in an 18 inch Vigreux column; andup'on removalof watenthe pressure:

was reduced to 20 mm. Distillation was con tinued and.37.2parts of a product identified as propionamidewas. collected at 118? basedxupon. the amount of. dien-propyl monosulfidefed into the reaction.

Example 4.-'In a manner similar to Example 3 -additional. reactions were carried out, and the results-are tabulated in Table II.

Since the propylene-sulfur oil-i Example 3.--The reaction of this examplewas C. The amount. of. amide represented 51. mol per; cent,

TABLE 11 Reaction of alkyl sulfides withsulfur and ammonia igi'ielci i 1 Yielgl of ropionroplomc Water 535 Sulfur Ammonia Reaction ReaPtion m 4 AC1 Alkyl Sulfide sulfides (M015) Sulfide (M015) (M015) Tenzpejrature Pervcgngiby Pegziengfby (M015) a, allryl sulfide sulfide di-n-propyl disulfidc '0. 5 2. 75 0. 6 2. 2 l. 4 252-265 1.0 54 Do 0. 5 2. 75 0. 6 1.2 1.4 256-265 0. 57 I 14 Do 0.5 I 2.75 0.08 1.7 1. 4 258*260 0.25 71. 5 l2 di isopropyl disulfide O. 124 0. 68 0.15 0. 54 0. 258-266 1. 0 61 Example 5.-A sulfur-containing oil was prepared by reacting a mixture of the" following materials in a pressure tube lined with stainless steel. Agitation of the tube was accomplished by placing it in a rocker assembly equipped with band heaters.

Parts Aqueous ammonia (28% ammonia) 150 Sulfur '64 Isobutylene 60 Pyridine 100 The above mixture was heated for 4 hours at a temperature between 150 C. and 160 C. The tube was cooled to room temperature, gaseous products (essentially Has) were bled off, and the liquid portion separated into two layers. The top layer was a. light orange oil, and the bottom layer was the aqueous portion.

A composite of oils obtained from a number of runs identical to the one described above was distilled from a distilling flask at a temperature between 180 to 190 C. The distillate was then fractionated using a two-foot column packed with glass helices using a total reflux partial take-off head. Distillation was carried out at a pressure of 1 mm., and the following fractions were collected and separated:

compared with the known physical data for isobutyl di'su'l'fide and isob'utyl trisulfide respectively, fraction 1 was concluded-to be isobutyl disul fide and fraction 3 was concluded to be isobutyl trisulfide.

On the basis of the above analysis fraction 2 was concluded to be a mixture of isobutyl disulfide and isobutyl tr i'sulfide. A mixture of 30 parts of fraction 2, 64 parts of sulfur, 75 parts of aqueous ammonia (28% ammonia), and parts of pyridine was introduced into a stainless steel hydrogenation bomb equipped with iron gaskets. Agitation of the bomb was accomplished by placing it in a rocker assemblyequi'pped with band heaters. The mixture was agitated at about 220 C. for 4 hours. The bomb was cooled to room temperature, and hydrogen sulfide formed during therea'ction Was bled off. lihe liquid product was acidified with hydrochloric acid and filtered immediately. The filtrate was extracted continuously with ethyl ether for 20 hours to give '16 parts of a semi-solid upon evaporation of the ether. This-extract was dissolved inmore ether, treated with a decolorizing carbon, dried over sodium sulfate, filtered, cooled in a Dry Ice-meth anol mixture, and filtered. A very light yellow solid ('7 parts) was collected and identified as isobutyramide, M.'P-.:129 to 130 C. The yield Boiling Parts of Refractive Fraction Number Range, Each Index, Colorv C. Fractionv 20 C.

20. 2 l. 4878 Very light yellow.

17.3 1. 520 Do. 4 14. 6 1.5200 Darker yellow. Residue 26. 3 l. 5200 Orange.

The following physical constants were determined for the first fraction:

Calculated for Fraction No. 1 Isobutyl Disulfide Molecular Refracti0n53.6 53. 2 Percent Sulfur34.5 35. 9 Percent Carbon-54.3 53. 9 Percent Hydr0genl0.3 10.18

The following physical constants were determined for the third fraction:

Calculated for On the basis of the close compariso'npf the above hysical constants for fractions land 3 of amide, based upon the weight of a mixture of isobutyl disulfide and isobutyl trisulfide, was about 28mol percent.

It is to be understood that the foregoing examples are illustrative but are not intended to limit the invention. Thus, in Example 5, di iso butylene can be employed in place of isobutylene, and the resulting disulfide can be converted to amide in the de'scribed'manner.

If desired, molten sulfur may be introduced into the reaction vessel along with water, any monia and hydrogen sulfide. Alternatively, a clear ammonium polysulfide solution may be prepared by adding the sulfur, water, ammonia and hydrogen sulfide in suitable proportions to form a homogeneous liquid (1 sulfide ion can solubilize 4 sulfur atoms), which homogeneous liquid can be injected into the reaction mixture along with propylene, or through a separate feed line. Still another method is to introduce ammonia, water and sulfur, without hydrogen sulfide; these ingredients can be introduced separately, if desired.

Depending upon the :end product desired, the

reaction may be carried out in the presence of the inert solvent in the presence of water. If water is omitted, the carboxylic acid derivative is a thioamide. The use of a suitable solvent such as dioxane, pyridine, etc., is permissible but is usually not essential. Such inert solvents may be employed to render complex mixtures of reactants homogeneous and reduce the total vapor pressure of the heated reaction mass.

It is within the scope of the present invention to employ dialkyl sulfides in which different alkyl groups are in the molecule.

As the reaction temperature is increased, the rate of reaction increases, but the severity of degradation of the starting material increases and cleavage of car-bon-to-carbon bonds occurs. Because elevated temperatures are required for amide formation, the reaction, is carried on in a closed system to avoid loss of the reactants from the reaction medium by vaporization. Consequently, in the absence of applied pressure, the pressure of the system will vary with the temperature of the reaction and the volatility of the reactants or the reaction medium.

The proportion of dialkyl sulfide to the other reactants may be varied Widely. To obtain good yields of carboxylic acid amides, a slight excess of ammonia is required over that which is chemically equivalent to the amount of alkyl sulfide. For example, 3 mols of ammonia per mol of dialkyl sulfide have given good yields of amides, and at least 2 moles of ammonia per mol of dialkyl monoor di-sulfide is generally used. The amount of sulfur to be used should be as low as possible in most instances to decrease the probability of side reactants and increase the ease of processing the mixture of reaction products. It has been found that the reaction proceeds rapidly with good yields in the presence of an amount of sulfur in excess of that chemically equivalent to the amount of alkyl sulfide. It takes 2.5 atoms of sulfur, either as elemental sulfur Or as sulfur in sulfide, to react with each alkyl radical. Accordingly, the amount of sulfur required to be added as ammonium polysulfide is not as high when the sulfide reactant is a disulfide as when it is a monosulfide.

The quantity of water initially present should be sufficient to convert any thioamide to carboxylic amide, and to facilitate handling the liquid reaction product. For example, 2 mols of water are necessary to react with one mol of dialkyl dior mono-sulfide, and at least one additional mol of water is necessary to prevent formation of a thioamide and any other by-products and also contribute to making the reaction product sufficiently liquid to maintain the solid reactants and products in solution. The use of less than about 3 mols of water per mol of alkyl sulfide results in the formation of appreciable amounts of thioamide, other by-products, and excessive amounts of degradation products. Further, a water concentration below 3 mols per mol of alkyl sulfide makes handling of ammonium hydrosulfide formed difficult and thereby complicates the recovery process. On the other hand, a water concentration of about 6 to 10 mols per mol of alkyl sulfide contributes an excessive volume of liquid to be processed. The optimum amount of water recommended for the present process ranges from about 3 to 6 mols per mol of alkyl sulfide.

From the foregoing, it will be appreciated that the proportions of reactants present may be varied, as reaction will take place in the presence of the rate of the reaction and the approachof the yield to theoretical being affected as proportions are varied. Further, the considerations with respect to the proportions are equally applicable whether a mixture of sulfur and ammonia is used or yellow ammonium polysulfide. Small amounts of hydrogen sulfide, up to 1 mol per mol of alkyl sulfide, may be added initially to the mixture of ammonia and sulfur to dissolve the sulfur and promote rapid formation of a-homogeneous reaction solution containing ammonium polysulfide.

The process of the invention is especially useful in the manufacture of propionamide and isobutyramide which are in turn highly valuable as intermediates in the manufacture of other useful chemicals.

I claim:

l. A process for preparing amides of aliphatic carboxylic acids which comprises heating a dialkyl sulfide of the formula alkyl(S) nalkyl wherein n is an integer of from 1 to 2 inclusive with aqueous ammonium polysulfide at a temperature within the range of 180 C. and 340 C. under superatmospheric pressure, whereby an aliphatic carboxylic acid amide is produced and thereafter separating the said amide from the resulting mixture.

2. A process for preparing amides of aliphatic carboxylic acids which comprises heating an alkyl sulfide of the formula alkyl(S)nalkyl, wherein n has a value of from 1 to 2 inclusive, with aqueous ammonium polysulfide at a temperature within the range of 240 to 340 C. under superatmospheric pressure, whereby an aliphatic carboxylic acid amide is produced and thereafter separating the said amide from the resulting mixture.

3. Process of claim 2 wherein the said alkyl sulfide is di-n-propyl monosulfide.

4. Process of claim 2 wherein the said alkyl sulfide is di-n-propyl disulfide.

5. Process of claim 2 wherein the said alkyl sulfide is di-isopropyl disulfide.

6. Process of claim 2 wherein the said alkyl sulfide is di-isobutyl disulfide.

7. A process for preparing amides of aliphatic carboxylic acids which comprises heating an alkyl sulfide of the formula alky1(S)nalkyl,

wherein n has a value of from 1 to 2 inclusive and the total number of carbon atoms per molecule is from 6 to 13 inclusive, with aqueous ammonium polysulfide at a temperature within the range of 240 C. to 340 C. under superatmospheric pressure, the quantity of water present being from. 3 to 6 mols per mol of alkyl sulfide, the quantity of ammonia, free and combined, being from 2 to 3 mols per mol of alkyl sulfide, whereby an aliphatic acid amide is produced and thereafter separating the said amide from the resulting mixture.

8. A process for the synthesis of alkanoic acid amides which comprises heating a reaction mixture comprising an alkene and aqueous ammonium polysulfide at a temperature within the range of C. to 300 C. whereby an alkanoic acid amide and an alkene-sulfur oil is obtained,

amide is obtained, and thereafter separating a1- kanoic acid amide from the resulting mixture.

9. A process for the synthesis of propionamide which comprises heating a reaction mixture comprising propylene and aqueous ammonium polysulfide at a temperature within the range of 140 C. to 300 C. whereby propionamide and a propylene-sulfur oil is obtained, separating propionamide and propylene-sulfur oil from the resulting mixture, and thereafter heating the said propylene-sulfur oil at a temperature within the range of 200 to 350 C. in a reaction mixture comprising aqueous ammonium polysulfide, whereby an additional quantity of propionamide is obtained, and thereafter separating propionamide from the resulting mixture.

10. The process of claim 9 wherein the formation of propionamide from the propylene-sulfur oil and ammonium polysulfide is carried out at a pressure of at least 2,000 lbs/sq. in.

11. The process of claim 9 wherein the formation of propionamide from the propylene-sulfur oil and ammonium polysulfide is carried out at a pressure of 3,000 to 5,000 lbs/sq, in.

12. The process of claim 9 in which the formation of propionamide from the propylene-sulfur oil is carried out at a pressure of at least 2,000 lbs/sq. in. and the reaction mixture comprises at least 1.5 mols of ammonia and at least 2 mols of water per mol of propylene.

13. The process of claim 9 in which the formation of propionamide from the propylene-sulfur oil is carried out at a pressure of at least 2,000 lbs/sq. in. and the reaction mixture comprises at least 1.5 mols of ammonia, includin ammonia combined as ammonium polysulfide, at least 2 mols of water and from 2 to 6 mols of free and combined sulfur per mole of propylene.

14. The process of claim 13 in which the quantity of water is from 2 to 6 mols per mol of propylene.

MARCUS A. NAYLOR, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,051,806 Allen Aug. 25, 1936 2,459,706 King Jan. 18, 1949 2,495,567 Carmack Jan. 24, 1950 

1. A PROCESS FOR PREPARING AMIDES OF ALIPHATIC CARBOXYLIC ACIDS WHICH COMPRISES HEATING A DIALKYL SULFIDE OF THE FORMULA ALKYL(S) N ALKYL WHEREIN N IS AN INTEGER OF FROM 1 TO 2 INCLUSIVE WITH AQUEOUS AMMONIUM POLYSULFIDE AT A TEMPERATURE WITHIN THE RANGE OF 180* C. AND 340* C. UNDER SUPERATMOSPHERIC PRESSURE, WHEREBY AN ALIPHATIC CARBOXYLIC ACID AMIDE IS PRODUCED AND THEREAFTER SEPARATING THE SAID AMIDE IS PRODUCED AND THEREING MIXTUE. 